In the field of semiconductor device manufacturing, techniques are in demand for increasing the density of semiconductor devices through microfabrication. For example, there is a demand for an etching process for forming a hole with a relatively small diameter of 10-20 μm at a depth of at least 100 μm on a silicon (Si) substrate.
Also, recently, attention is being directed to the so-called three-dimensional (3D) packaging technique that involves stacking semiconductor chips to increase the density per unit area of semiconductor devices. An example of the 3D packaging technique includes 3D circuitization, which involves establishing electrical connection between semiconductor chips stacked on each other using an electrode formed at a through hole (TSV: through-silicon via) penetrating through a semiconductor chip. An etching process for etching a deep hole penetrating through the semiconductor chip has to be performed in such case.
In the etching process as described above that may be implemented in a plasma etching apparatus, for example, a plasma processing method is known that involves temporarily and intermittently stopping the supply of SF6 gas that encourages etching for a short period of time and forming a nitride film on a surface of a silicon substrate while the etching process is temporarily stopped in order to etch the silicon substrate without the occurrence of undercutting (see e.g. Patent Document 1).
However, in the case of forming a hole with a depth of at least 100 μm, plasma etching has to be performed for a long period of time. Also, in view of the recent demands for further miniaturization of semiconductor devices, holes with relatively small diameters of 10-20 μm have to be formed. With the demand for further miniaturization of the semiconductor devices, the thickness of a resist film has to be reduced in order to secure shape accuracy. Also, the etch rate of a silicon layer with respect to the etch rate of the resist layer; namely, the selectivity, may not be adequately high. Thus, when plasma etching is performed for a long period of time, a mask may be removed before the etching process is completed, for example.
In this respect, a plasma processing method is known that involves alternately repeating a deposition step of performing a plasma process on a substrate by supplying a gas having a high deposition gas content and an etching step of performing a plasma process on the substrate by supplying gas with a high etching gas content (see e.g. Patent Document 2).
In a plasma process that involves repeatedly performing a deposition step and an etching step as described above, the selectivity of the substrate with respect to the resist film may be higher compared to the case of performing a normal plasma etching process, and a desired etching shape may be efficiently formed while maintaining a relatively high etch rate.